Los neumáticos fuera de uso (NFU)

The Bayou Corne sinkhole in Assumption Parish, LA was used as a case study to develop the model to understand risk of cavern collapse on mined salt domes. An analysis of subsidence/ground movement using UAVSAR data was conducted beginning with the initial signs of precursory surface deformation, through sinkhole formation and ending with the last data collection in 2014. Subsidence was mapped through analysis of raster UAVSAR images with a phase component (i.e. interferograms). The phase component was translated into a subsidence measurement using the wavelength of the radar (24cm). Interferograms were then analyzed to detect ground level change (i.e. subsidence) and map the change in elevation over the time period. Subsidence contours were then analyzed in the context of local geology, mining design and activity. Finally, a model for sinkhole formation hazard on mined salt domes was generated from the results.

Specific Tasks

1) Data acquisition (Figure 4.1)

a. InSAR raster scenes with phase data created by NASA JPL (Table 1) b. Supporting data collected or created and compiled (Table 2)

i. Geologic data ii. Land cover (LC) data iii. Sinkhole growth surveys iv. Mining data

2) Data preprocessing/processing: Defining the Case Study Area (Figure 4.1) a. Define geologic setting of Napoleonville Salt Dome

i. Thickness of [salt dome] overlying surficial material ii. Depth to clay confining layer

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b. Define subsurface topography of salt domes i. Depth to top of salt

ii. Salt dome shape (location of edge of salt) c. Define anthropogenic activity

i. Well depths

ii. Type of activity (e.g. solution mining, brine or petroleum storage) iii. Land cover (vegetated, barren, water or urban/developed)

d. Measure subsidence using InSAR data 3) Data analysis/modeling (Figure 4.1)

e. Correlate subsidence to the geologic and anthropogenic inputs

f. Weight relevant factors affecting subsidence and generate spatially oriented decision model

4) Test model using the 53 mined caverns on the Napoleonville Salt Dome and the known collapse of Oxy-Geismar Well 3 (Figure 4.1)

Table 4.1. UAVSAR InSAR Pairs for Napoleonville Salt Dome (NASA Jet Propulsion Laboratory,

2015)

--- Data take 1 --- --- Data take 2 ---

Mode Flight ID Data take ID Date Acquired Flight ID Data take ID Date Acquired

InSAR 11038 7 2011-06-23 12053 12 2012-07-02 InSAR 12053 12 2012-07-02 12115 9 2012-10-26 InSAR 12115 9 2012-10-26 13053 2 2013-04-03 InSAR 13053 2 2013-04-03 13134 4 2013-07-24 InSAR 13134 4 2013-07-24 13163 4 2013-10-29 InSAR 13163 4 2013-10-29 14036 7 2014-04-09 InSAR 14036 7 2014-04-09 14161 7 2014-10-28

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Figure 4.1. Research Methods Flowchart

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Table 4.2: Data Sources (NASA Jet Propulsion Laboratory, 2015; Louisiana Department of Natural Resources, 2015; Louisiana

Department of Natural Resources, 2015; PBEnergy Storage Services, Inc., 2013; United States Geologic Survey, 2015) (United States Geologic Survey, 2015)

Data Type Date File Name Source Online Access

Background imagery

.jpegs digitized to rasters

Varied Varied Google Earth NA

UAVSAR InSAR data

raster with phase data

2011-2014 Varied NASA JPL http://uavsar.jpl.nasa.g

ov/cgi-bin/data.pl

Napoleonville Salt Dome contours

Paper map 2013 Napoleonville Salt

Structure Map and Cavern Maximum Radii

Louisiana Department of Natural Resources Office of Conservation Mining and Injection Division

None – available in paper copy at LDNR in Baton Rouge, LA Mining/well locations ArcGIS shape/layer file 2007-2014 oil_gas_wells_LDNR_2007 .shp Salt_Dome_Caverns.shp

Louisiana Department of Natural Resources GIS Download Area

http://sonris-

www.dnr.state.la.us/gis /dnld/download.html

Mining/well data Tabular – individual well info (e.g. coords) accesible by hyperlink

2014 NA Louisiana Department of Natural

Resources Office of Conservation

http://sonlite.dnr.state.l a.us/sundown/cart_pro d/cart_con_injwlbypsh2

Overlying geology .pdf 2013-2014 StructureContourIsopach. pdf

Louisiana Department of Natural Resources

NA – received via email Subsurface mining

cavern boundaries

Paper map 2013 Napoleonville Salt

Structure Map and Cavern Maximum Radii

Louisiana Department of Natural Resources Office of Conservation Mining and Injection Division

None – available in paper copy at LDNR in Baton Rouge, LA Land cover 30m raster 2014 Generated from LANDSAT

8 OLI imagery

USGS Global Visualization Viewer (GLOVIS)

http://glovis.usgs.gov/

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Step 2: Defining the Case Study Area: Overlying Geology, Salt Structure and Mining Activity The intent of this study was to create a functional tool that municipalities with limited resources (e.g. computing/GIS capabilities and personnel) may use to estimate the risk for subsidence on mined salt domes and identify potentially hazardous areas that warrant further investigation (e.g. collection of UAVSAR data or installation of GPS reference stations). For this portion of the research, spatial analysis was conducted in ArcMap™ 10.2.2 (Figure 4.1). Data for all variables were extracted to raster surfaces with identical grids covering the top of the salt dome. The resulting grid for each attribute had approximately 6.5 million 5’ by 5’ cells, each with an, attribute specific value. The potential range of values for each attribute was then indexed into five categories (high risk = 5, high moderate risk = 4, moderate risk = 3, low moderate risk = 2 and low risk = 1) and assigned a value based on the assessed risk for subsidence/collapse (e.g. for land cover: standing water = high risk = 5 and impervious cover = low risk = 1). When possible, break points for risk classes were identified from state (Louisiana Department of Natural Resources Office of Conservation, 2015) (Louisiana Department of Natural Resources office of Conservation, 2015) or international (Warren, 2006) regulations governing mined salt domes. The map algebra feature (Figure 4.2) in ArcMap™ was then used to weight the influence of each variable (initially in the absence of subsidence data) and calculate an overall risk value for each cell. Resulting total risk values were mapped and compared to historic subsidence as estimated from UAVSAR InSAR data.

(Proximity to edge of salt*.3) + (Mining activity*.19) + (Proximity to other caverns*.14) + (Cavern volume*.13) + (Depth to salt*.1) + (Thickness of confining layer*.1) + (Land cover*.04) = risk level ranging from 1 to 5

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Overlying Geology and Salt Structure

Three geologic attributes of the NSD were identified as having impact on the potential for collapse: location of the edge of the salt, depth to the top of salt and depth to the base of the clay confining layer. Since the NSD, and many other salt domes, are somewhat bulb shaped (i.e. larger at the top that at the bottom), three dimensional modeling of the salt contours is likely not possible in a local government GIS division. To overcome the issues that accompany creating a three-dimensional representation of the salt dome, the edge of salt contour and extents of the underground caverns were mapped in two-dimensional space. While avoiding 3D surface modeling for some attributes will introduce a degree of error, it will still allow for the model to serve as a functional tool for municipalities with limited GIS/computing capacities.

The edge of salt contour was defined as the most restrictive contour (i.e. smallest polygon) created from multiple salt dome depth contour lines (largely the -1000’ and -7000’ on Figure 4.3). The “near” function in ArcMap™ was then used to assign a distance from the most restrictive salt edge contour to each of the 6.5 million cells in the gridded surface. The processing extent and cell size/mask for the edge of salt contour near analysis (and all other attribute layers) was modified to coincide with the study’s 6.5 million cell gridded surface. Based on distances identified in Louisiana Administrative Code (LAC) 43:XVII governing salt solution mining and hydrocarbon storage (Chapters 33 and 3 respectively), risk categories for the proximity to the edge were established (Table 4.3) and mapped (Figure 4.4).

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Figure 4.3. Most restrictive edge of salt contour

Table 4.3. Break points for risk associated with proximity to the edge of salt

 <100’ (<30.48m) = High Risk (5)

 100.01’ – 200’ (30.49 – 60.96m) = High Moderate Risk (4)  200.01’-250’ (60.97 – 76.2m) = Moderate Risk (3)

 250.01’-300’ (76.3 – 91.44m) = Low Moderate Risk (2)  >300’ (>91.44m) = Low Risk (1)

Most restrictive edge of salt contour

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Figure 4.4. Proximity to the Edge of Salt on the Napoleonville Salt Dome

The depth to the confining layer surface utilized interpolated stratigraphy data obtained from over 75 wells recorded in a structure contour map developed by the Louisiana Department of Natural Resource (LDNR) (Table 4.2). The data extracted from the LDNR structure contour map provided base of clay elevation at most of the wells on the NSD. Data for the depth to top of salt elevations were extracted from the LNDR’s Napoleonville Salt Structure Map for each of the 53 cavern locations (Figure 4.3). The two layers of elevation data (in feet below the surface) were extracted from the LDNR map and recorded in tabular form in Microsoft® Excel®. Most well locations did not contain data for every layer (e.g. depth to salt and base of clay). Therefore, the